Plating on plastic processes for decorative and electromagnetic impedance shielding purposes are widely used in the industry. Said processes are applied to various plastic parts such as shower heads, mobile phone covers and radiator grills. One main process route involves an electroless plating step after pre-treatment and activation of the plastic substrate to be coated. The electroless plating methods applied are usually electroless deposition of copper or nickel. The metal or metal alloy layer deposited onto the activated plastic substrate serve as a full area conductive surface for further metal layers deposited later by electroplating methods. The main plastic materials used for said purpose are ABS (acrylonitrile-butadiene-styrene copolymer), ABS/PC blends and PA. The main electroplating processes applied after electroless deposition of copper or nickel are plating of copper, nickel and finally chromium. Such methods are well known in the art and for example described in EP 0 616 053 B1.
In case a nickel alloy is deposited by an electroless plating method the requirements for the electroless nickel plating process and the nickel plating bath used are manifold.
Electroless nickel plating baths capable for deposition of nickel phosphorus alloys having a phosphorus content in the range of 4 to 11 wt.-% are known in the art.
An electroless nickel plating bath useful for deposition of nickel phosphorous alloys onto conducting SnO2 surfaces is disclosed in US 2002/0187266 A1. Said electroless nickel plating bath may contain thiosalicylic acid as a stabilizing agent. However, disclosed plating temperatures are as high as 70° C. and the plating bath requires hazardous substances such as lead ions.
An electroless nickel plating bath comprising sulphide ions together with a sulphide ion controller is disclosed in U.S. Pat. No. 2,762,723. Compounds suitable as sulphide ion controller are selected from inorganic sulphides, other thio compounds, bismuth and lead ions.